ABS drain leaks

I just installed a washing machine hookup and drain at my girlfriend's apartment.

All went well with the water hookups, t-ing off the copper lines.

For the drain, I wound up redoing the drain under the sink with a Y and T and connecting the washing machine drain through the wall just past the sink trap. This was my only option as it was the only exposed drain to work with, and everything else was cast iron.

First I had a leak in the middle (where I had connected the two drains at the very end), wound up chopping it out and redoing it, then somehow by fixing that I must've cracked a threaded bit at the end. I chopped out the end, put on a new piece (this time without cranking it down with a wrench, but I did use lots of pipe dope), and now that leaks again.

To redo this means literally ripping everything out to the pipe above the sink trap and redoing it all, because there is virtually no exposed pipe to work with, just glued fittings.
It's a 1.5" female threaded bit that goes onto male threads that are reduced from a larger cast iron pipe I don't want to mess with.

Anyway, the leak is so small that I may just leave it it, or goop it or something.

Is this the kind of leak that eventually will clog itself? Or will it get worse? Should I redo it?